F-I. Chen et aL/ Engineering Failure Analysis 37 (2014)29-41 d Fig 10. Appearance of tube 1B160012-14(a)o(b)90(c)180(d)270(e)S-shaped furrow crack magnified from(b) the surrounding wear scratches. So it should have been created by adhesive wear by the irregular motion of a hard adhering to the surface of the titanium tube in micro-vibration. The width of the crack is about 255-285 um(Fig. 11 define it more accurately it is three-body wear between the hard particle, the outer wall of the titanium tube internal boring, and it is also a kind of concentrated wear. 3.2.3. Micro-morphology and component analysis Fig 12 presents the surface micro-morphology of the titanium tube. Scratches in the wear zone are somewhat directional ( Fig. 12(b)), and there is layered deposit on the tube wall( Fig. 12(b)). EDS results of the deposit is shown in Fig. 13 and Table 3. The deposit mainly consists of iron oxides. 4. Discussion of failure mechanisms corosion The black deposit on the surface of titanium tubes has proved to be Fe3 O4. which comes from the galvanic corrosion of arbon steel support plates under oxygen-deficient condition. It is commonly hat there is a compact oxide film on the surface of pure titanium, which raises its electrode potential from-1.63 to 0.0V[15]. As a result, carbon steel whose electrode potential is-0.6V[15, will be the anode during galvanic on. The half-cell and total reactions arethe surrounding wear scratches. So it should have been created by adhesive wear by the irregular motion of a hard particle adhering to the surface of the titanium tube in micro-vibration. The width of the crack is about 255–285 lm (Fig. 11(b)). To define it more accurately, it is three-body wear between the hard particle, the outer wall of the titanium tube, and the internal boring, and it is also a kind of concentrated wear. 3.2.3. Micro-morphology and component analysis Fig. 12 presents the surface micro-morphology of the titanium tube. Scratches in the wear zone are somewhat directional (Fig. 12(b)), and there is layered deposit on the tube wall (Fig. 12(b)). EDS results of the deposit is shown in Fig. 13 and Table 3. The deposit mainly consists of iron oxides. 4. Discussion of failure mechanisms 4.1. Galvanic corrosion The black deposit on the surface of titanium tubes has proved to be Fe3O4, which comes from the galvanic corrosion of carbon steel support plates under oxygen-deficient condition. It is commonly known that there is a compact oxide film on the surface of pure titanium, which raises its electrode potential from 1.63 V [14] to 0.0 V [15]. As a result, carbon steel, whose electrode potential is 0.6 V [15], will be the anode during galvanic corrosion. The half-cell and total reactions are as follows: Fig. 10. Appearance of tube 1B160012-14 (a) 0 (b) 90 (c) 180 (d) 270 (e) S-shaped furrow crack magnified from (b). 36 F.-J. Chen et al. / Engineering Failure Analysis 37 (2014) 29–41